The present invention relates to gas turbine engines, and more particularly, to integrally bladed disks in gas turbine engines.
The fan, turbine and compressor sections of gas turbine engines include one or more circumferentially extending rows or stages of airfoils, commonly called rotor blades, which are axially spaced between rows or stages of fixed airfoils (stator vanes). The rotor blades are connected to and extend radially outwardly from a rotor disk. During operation the centrifugal loads generated by the rotational action of the rotor blades must be carried by the rotor disk within acceptable stress limits.
Conventional rotor blades are carried in the rotor disk by a dovetail or fir tree root which slides into and interlocks with a corresponding dovetail slot in the perimeter of the rotor disk. However, as the number of rotor blades around the perimeter of the disk increases, insufficient material is available for supporting the plurality of rotor blades within acceptable stress limits. Accordingly, integrally bladed disks have been developed and are commercially used. Integrally bladed disks do not utilize the interlocked dovetail design but instead are integrally joined to the rotor blades as a single-piece, unitary assembly by milling, forging, casting or other known manufacturing operations.
Integrally bladed disks can be used to increase aerodynamic efficiency of the gas turbine engine while reducing the stresses associated with supporting the rotor blades. One of the stresses associated with supporting the rotor blades is a hoop stress. The hoop stress is defined as a load measured in the direction of the circumference of a rotating body, the load being created by thermal gradients and centrifugal forces acting in a radial direct outwardly from the axis of rotation of the body. The hoop stress is particularly acute where the gas turbine engine utilizes integrally blades disks. Integrally bladed disks have been known to develop fractures along their perimeter during operation due to the hoop stress and principle stresses. These fractures necessitate replacement of the integrally bladed disks to avoid a catastrophic failure.